1. Field of the Invention
The present invention relates to diffusion transfer photographic light-sensitive materials and, more particularly, to an element for a diffusion transfer photographic light-sensitive material having a carboxylic acid polymer layer with improved physical properties.
2. Description of the Prior Art
In a diffusion transfer photographic light-sensitive material, it is known the photographic image produced therein can be stabilized by incorporating a carboxylic acid polymer layer as a coated layer into the photographic material, neutralizing the alkali remaining in the system at the appropriate time after the effects of development and other processings have been completed, and extracting other salt-forming components with the carboxylic acid polymer layer to prevent their precipitation and deposition in the photographic material, as disclosed in U.S. Pat. Nos. 3,362,819 and 3,362,821.
The carboxylic acid polymer layer must contain acid groups in an amount sufficient to neutralize the alkali contained in the system after processing and return the system to neutrality. However, a carboxylic acid polymer layer which has acid groups in the salt form after the neutralization has a markedly increased hydrophilic property. Further, a carboxylic acid polymer layer with a high content of acid groups is hydrophilic as such and this layer swells markedly after the neutralization due to the increase in hydrophilic character, resulting in the occurrence of reticulation or a dissolution of the layer. Restricting the amount of the carboxyl groups present, mixing the carboxyl group containing polymer with other polymers or the introduction of a hydrophobic residue, for example, esterification of a part of the carboxyl groups, in order to reduce the hydrophilic property to below a certain level, results in disadvantages such as the carboxylic acid polymer layer thickness must be increased to incorporate a fixed amount of carboxylic acid groups per unit area, the capacity of neutralizing alkali is decreased, or an organic solvent must be used to dissolve the carboxylic acid polymer which requires facilities for preventing hazards such as explosions during production.
Attempts have been made to harden to polymer layer having a high content of carboxylic acid groups using a cross-linking agent, for example, a compound containing, in the same molecule, at least two functional groups selected from an aziridyl group, a glycidyl group and an epoxy group, e.g., as described in British Pat. No. 1,495,464, an alum such as chromium alum, potassium alum, etc., as described in C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Third Edition, Macmillan, New York (1966), an isooxazolium salt in combination with gelatin as described in U.S. Pat. No. 3,619,236, a carbodiimide, a dihydroquinoline-N-carboxylic acid ester as described in U.S. Pat. No. 4,013,468, a bisisooxazolium as described in Belgian Pat. No. 697,493, etc.
These compounds, however, have various subsidiary disadvantages. For example, an alum, a carbodiimide and an aziridine derivative have a strong toxic action on the human body, an epoxy compound has an adverse effect on the photographic properties, and the preparation of an isooxazolium is so difficult that the compound is very expensive. More importantly, in addition to these disadvantages, it should be noted that it is difficult to obtain a sufficiently hardened carboxylic acid polymer layer by addition of such a cross-linking agent to a carboxylic acid polymer even when the amount of addition of the cross-linking agent is increased, and when these cross-linking compounds are used in a large amount, undersirable influences are observed such as reduced diffusion of dyes from the light-sensitive layer of a diffusion transfer photographic material, a change in sensitivity, the carboxylic acid polymer layer per se becomes brittle or colored, and the like.